The objective of the present project is to study deletions of the short arm of chromosone 9 found in human leukemia cell lines and in primary human leukemia cell samples. These deletions include the entire interferon gene cluster which is located at bands 9p21p22 and is composed of the beta interferon gene and about 30 alpha and alpha-like interferon genes and pseudogenes. These deletions are frequently submicroscopic in at least one chromosone 9 homologue. DNA sequences from inside the deleted regions, or surrounding them, will be cloned from genomic libraries enriched for very large restriction fragments that contain these sequences. These cloned DNA sequences will be used to map the deletion breakpoints and to examine their gene content. The breakpoint sequences will be cloned and analyzed to look for clues about the possible mechanism of deletion. As in the cases of retinoblastoma and Wilms' tumor, these deletions may result in the loss of a tumor suppressor gene or genes. Interferons have antiproliferative effects on various cell types. Since some of these effects are mediated by an autocrine mechanism, the interferon genes may be the tumor suppressor genes lost with the deletions of 9p. To test these hypotheses, the deleted chromosome region will be reintroduced into the "deletion" cell lines by chromosome mediated gene transfer. In other experiments, cloned interferon genes will be transduced into the "deletion" cell lines using retroviral vectors. The transfected or transduced cells will be compared to the original cell lines, with respect to their tumorigenicity in nude mice and growth properties in vitro. The effect of interferons on the growth of the "deletion" cell lines also be studied. The proposed studies may be of relevance to biology of human leukemia, in revealing a new mechanism involved in leukemogenesis. This mechanism may be of importance in the initiation or progression of the disease, and it may have consequences for its diagnosis, prognosis and treatment.